The embodiments described herein relate generally to control of a power generation system coupled to a power grid, and more specifically, to monitoring an impedance of the power grid during operation of the power generation system.
Solar energy has increasingly become an attractive source of energy and has been recognized as a clean, renewable alternative form of energy. Solar collector systems utilize a plurality of photovoltaic (PV) arrays to convert solar energy incident on the PV arrays into direct current (DC) power. Typically, the DC output of the PV arrays is coupled to a DC to alternating current (AC) inverter to convert the DC output of the PV arrays into a suitable AC waveform that can be fed to a power grid. Furthermore, the AC output of the DC to AC inverter may be provided to a transformer that increases the voltage of the AC power prior to applying the AC power to the power grid.
The AC power applied to the power grid is required to meet grid connectivity expectations. These requirements address safety issues as well as power quality concerns. The Institute of Electrical and Electronics Engineers (IEEE) has written a standard that addresses grid-connected distributed generation including renewable energy systems (IEEE 1547-2003). Underwriters Laboratories (UL) has also developed a standard, UL 1741, to certify inverters, converters, charge controllers, and output controllers for power-producing stand-alone and grid-connected renewable energy systems. UL 1741 verifies that inverters comply with IEEE 1547 for grid-connected applications.
Furthermore, a grid-connected PV power generation system may include low voltage ride through (LVRT), voltage regulation, and power factor correction capabilities. To support the grid voltage, the DC to AC inverter may also deliver reactive power to the power grid. Typically, a voltage level at a point of interconnection between the transformer and the power grid is measured, and the output of the DC to AC inverter is controlled based on the voltage level at that point of interconnection. However, this point of interconnection is not always accessible, or may not be accessible in an economical manner, and therefore, measuring the voltage level at the point of interconnection between the transformer and the power grid may be difficult or impossible.